title: Improvement in thermostability of metagenomic GH11 endoxylanase (Mxyl) by site-directed mutagenesis and its applicability in paper pulp bleaching process.
abstract: An attempt has been made for enhancing the thermostability of xylanase (Mxyl) retrieved from a compost-soil-based metagenomic library. The analysis of the structure of xylanase by molecular dynamics simulation revealed more structural fluctuations in β-sheets. When the surface of β-sheets was enriched with arginine residues by substituting serine/threonine by site-directed mutagenesis, the enzyme with four arginine substitutions (MxylM4) exhibited enhanced thermostability at 80 °C. The T 1/2 of MxylM4 at 80 °C, in the presence of birchwood xylan, increased from 130 to 150 min at 80 °C without any alteration in optimum pH and temperature and molecular mass. Improvement in thermostability of MxylM4 was corroborated by increase in T m by 6 °C over that of Mxyl. The K m of MxylM4, however, increased from 8.01 ± 0.56 of Mxyl to 12.5 ± 0.32 mg ml(-1), suggesting a decrease in the affinity as well as specific enzyme activity. The Mxyl as well as MxylM4 liberated chromophores and lignin-derived compounds from kraft pulp, indicating their applicability in pulp bleaching.
authors.affiliation: Department of Microbiology, University of Delhi South Campus, Benito Juarez, New Delhi, 110021, India, tsnarayana@gmail.com.
authors.forename: Digvijay Verma T
authors.initials: DV
authors.lastname: Satyanarayana
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D001120:Arginine / Q000737:chemistry / Q000235:genetics; D002384:Catalysis; D043364:Endo-1,4-beta Xylanases / Q000737:chemistry* / Q000235:genetics; D004795:Enzyme Stability; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D007218:Industrial Microbiology; D007700:Kinetics; D056186:Metagenomics; D056004:Molecular Dynamics Simulation; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010209:Paper; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D013696:Temperature
chemical_list: D011994:Recombinant Proteins; D001120:Arginine; D043364:Endo-1,4-beta Xylanases